To further confirm that Tppp3-expressing cells give rise to sarcomas, we also generated mice harboring Tppp3-CreERT2 allele and Rosa26-loxP-stop-loxP (LSL)-EWS/ATF1 allele (Rosa26Stop-E/A/Tppp3CreERT2) in which EWS/ATF1 can be induced in Tppp3-expressing cells upon tamoxifen treatment (Fig. 6c and Supplementary Fig. 6e, f). Here, EWSR1 is linked to sarcoma.